Various implantable medical devices for repairing or reinforcing cardiac and vascular structures have been developed in recent years. Some of these devices can be implanted inside a particular vascular or cardiac structure through so-called interventional, or endovascular, techniques. Interventional techniques involve surgically accessing the vascular system through a conveniently located artery or vein and introducing distal portions of a medical device assembly into the vascular system through the arterial or venous access point. Once the medical device assembly is introduced into the vascular system, it is threaded through the vasculature to an implantation site while proximal portions of the assembly having manually operated control means remain outside the body of the implant recipient. The medical device component of the assembly is then deposited at the implantation site and the remainder of the distal portion of the medical device assembly removed from the vascular system through the access point.
Exemplary interventional medical device assemblies include a catheter. The catheter can be used to precisely position the medical device at an implantation site as well as participate in deployment of the medical device at the implantation site. Some catheters have guidewires running their length to aid in positioning and deployment of the medical device. As an alternative to the guidewire, a catheter may be coaxial with an inner sleeve running inside the length of the catheter. The inner sleeve is used to hold an implantable medical device in position while the outer catheter is pulled back causing deployment of the device. Handles, knobs, or other manually operated control means are attached to the opposite end of the catheter in this type of assembly.
Some implantable medical devices, such as stents, stent-grafts, or other endoluminal devices often require reconfiguration from an initial compacted form to an expanded cylindrical configuration as the devices are deployed at an implantation site. These devices can expand on their own by virtue of the design and composition of their structural elements or through the use of an inflatable balloon placed inside the devices.
Self-expanding endoluminal medical devices are maintained in a compacted configuration in a variety of ways. Some devices are maintained in a compacted configuration by simply confining the compacted devices inside a catheter, or similar tool. Other devices are placed inside a sheath following compaction. In these assemblies, a control line is often used to assist in releasing the endoluminal device from the sheath.
In U.S. Pat. No. 6,352,561, issued to Leopold et al., a sheath is formed around an expandable endoluminal device and a control line used to maintain the sheath around the endoluminal device. The sheath is formed by folding a length of polymeric material in half and stitching the opposing edges together with the control line. The stitching pattern permits the control line to be removed from the sheath by pulling on a proximal end of the control line. As the control line becomes unstitched from the sheath, the endoluminal device is progressively released from confinement within the sheath. The control line is removed from the assembly as a distinct entity while the sheath remains at the implantation site.
In U.S. Pat. No. 5,647,857, issued to Anderson et al., an endoluminal device is held in a collapsed configuration over a catheter by a sheath. The assembly is provided with a control line having a free end and an end attached to a collar component of the catheter. The sheath is removed from the endoluminal device by pulling on the control line. As the control line is pulled, it cuts through and splits the sheath material from distal end to proximal end. As the sheath splits open, the endoluminal device is freed to radially expand. Unlike Leopold et al., the control line remains mechanically attached to the sheath and catheter assembly following deployment of the endoluminal device.
In U.S. Pat. No. 6,447,540, issued to Fontaine et al., a confining sheath is removed from around an endoluminal device with a control line that cuts through and splits the sheath material when pulled by a practitioner, much like Anderson et al. As with Leopold et al, the control line can be completely removed from the assembly as a distinct entity.
In U.S. Pat. No. 5,534,007, issued to St. Germain et al., a single-walled sheath that can collapse and shorten along its length is placed around a stent. As the distal portion of the sheath is retracted, it uncovers the stent. The uncovered stent is free to expand. A control line can be used to exert a pulling force on the collapsible sheath as a means of removing the sheath from the stent. The control line remains attached to the sheath during and subsequent to deployment of the stent.
In U.S. Pat. No. 6,059,813, issued to Vrba et al, a double-walled confinement sheath for an endoluminal device is described. In an assembly made of these components, the endoluminal device is placed over a catheter shaft in a collapsed configuration. An outer tube is placed in slidable relationship over the catheter. The distal end of the outer tube does not extend to cover the endoluminal device. Rather, the double walled sheath is placed over the collapsed endoluminal device. The inner wall of the sheath is attached to the catheter shaft near the proximal end of the endoluminal device. The outer wall of the double-walled sheath is mechanically attached to the outer tube. Movement of the outer tube relative to the catheter causes the outer wall of the sheath to move past the inner wall of the sheath. Movement of the outer tube in the proximal direction causes the sheath to retract and uncover the underlying endoluminal device. As the sheath retracts, the endoluminal device becomes free to expand. A control line is mechanically attached to the outer tube and serves to move the outer tube and retract the sheath.
None of these medical device assemblies utilize a control line that is integral with a sheath. Nor do these assemblies feature a sheath that is convertible to a control line as the sheath is removed from around an expandable medical device, such as an endoluminal device. Such an integral control line and confining sheath would preferably be made of a continuous thin-walled material or composite thereof. The thin-walled material would be flexible and exert minimal restrictions on the flexibility of an underlying expandable medical device. Thin-walled materials would also reduce the profile of the sheath and expandable medical device combination. An integral control line and confining sheath would simplify manufacture of control line-sheath constructs by eliminating the need to mechanically attach the control line to the sheath. An integral control line and confining sheath would also eliminate concerns regarding the reliability of the mechanical attachment of the control line to the sheath. Additionally, inclusion of materials, composites, constructions, and/or assemblies exhibiting compliance, compressibility, resilience, and/or expandability between the sheath-constrained expandable medical device and the delivery catheter would serve to cushion and retain the expandable medical device on a delivery catheter as well as assist in expansion of the expandable medical device in some embodiments.
In some medical applications, it would be advantageous to provide a deployment system or assembly to pre-pressurize an inflatable balloon, or other expandable mounting member, underlying an expandable medical device and maintain or increase the pressure in the balloon as a constraining sheath is gradually removed from the expandable medical device. This would allow for partial expansion of the expandable medical device at an implantation site and permit adjustments in the position of the device in a blood vessel before complete retraction of the sheath and final deployment of the device. In some embodiments, it would be advantageous to introduce a contrast medium into the balloon to provide a background against which an expandable medical device can be better visualized.
There is a need, therefore, for a deployment system or assembly that pressurizes and inflates an endoprosthesis mounting member-component of a catheter-based delivery system while simultaneously retracting a sheath-component of the delivery system from around an underlying expandable medical device.